1. Field of the Invention
The present invention relates to an injection molding machine, and in particular, relates to an injection molding machine including a mold rotating device.
2. Description of the Related Art
In general, an injection molding machine includes a mold and a molten resin is injected into the mold and then, mold clamping is performed for molding. When a mold closing or mold clamping is performed in the molding process, the mold closing or mold clamping is normally performed without the mold being rotated. However, when resins of a plurality of colors or a plurality of types are used for molding, it is necessary to rotate a movable side of the mold using a rotary table to inject resins of different colors or types.
When it is necessary to rotate the mold as described above, the stop of the mold after being rotated needs to be repeatedly positioned with precision to appropriately inject resins from any injection source. However, the influence of backlash increases with an increasing size of device and it may be difficult for an encoder provided in a drive motor to drive the mold alone to ensure the precision of positioning.
According to the technology disclosed for a micro film by Japanese Utility Model Registration Application No. 63-26620 (JP 1-132344 U), a rotational position of a rotary table is detected by a rotational position calculation device of the rotary table. Then, the rotary table is moved to a set rotation position by rotation in accordance with the resolution of a rotary encoder.
According to the technology disclosed by JP 2000-296532 A, the stop position is fine-tuned by a positioning unit in a mold rotating device provided with a positioning block in a lower portion of a table rotating device and a rotation portion is controlled to decelerate to a low-speed state from the rotation start and a high-speed state before being positioned in a final stop position where the positioning block and a stopper of the positioning unit are made to mechanically bump against each other.
According to the technology disclosed by JP 2014-121717 A, a servo motor that moves at least one of molds via a ram axis is included and a signal of an encoder of the servo motor or a signal of a linear sensor monitoring the position of the ram axis is used as control input to exercise feedback control of the position by the signal of the encoder in an interval in which the linear sensor cannot detect the position of the mold. The feedback control of position is exercised based on a signal of the linear sensor in an interval where the position of a mold can be detected by the linear sensor.
The technology disclosed for a micro film by Japanese Utility Model Registration Application No. 63-26620 (JP 1-132344 U) is a technology that gives feedback of positional information by mounting an encoder and an expensive device may be needed to mount the encoder. In addition, a measuring instrument needs to be incorporated into the device, which may make it difficult to retrofit the measuring instrument.
The technology disclosed by JP 2000-296532 A needs to mechanically adjust a positioning block to change the stop position, which may lead to difficulties of making correct adjustments in a short time.
The technology disclosed by JP 2014-121717 A uses control that uses a linear sensor and an encoder and thus can be applied only to linear movement of the mold.